The present invention relates generally to seals, and more particularly, to seals adapted for specialized, severe service applications.
One application for which there have been a large number of seals proposed is that of the so-called track pins on crawler tractor equipment. Crawler tractors usually include a pair of tracks, and each track is in turn made up of inner and outer chains of track links. A large plurality of links, typically 30 to 40 links, are assembled into an endless chain, and two such chains are then trained over the front idler roller and the rear sprocket final drive as well as over a number of suspension track rollers and track-carrying idler rollers. The inner and outer links in each chain are held together by track pins and bushings which extend through openings at either end of the track links. Track shoes or grouser plates extend transversely between the respective links on the inner and outer chains. These shoes or plates form the surface which rests on the earth and ultimately supports and forms the traction for the vehicle. Thus, the right and left hand vehicle tracks each include a plurality of plates, with the plates extending between and joining the links in the inboard chain to the links in the outboard chain.
Because track vehicles are particularly designed for use under severe conditions, namely, mud, sand, grit, ice and snow, rocky terrain, etc., and because the track is the portion of the vehicle which comes into the most direct and frequent contact with these severe conditions, track pins and their bushings are subject to rapid wear.
Numerous track pin seal designs have been proposed, and a number of them have been proved successful in use to a certain extent; however, most crawler vehicles either use no track pin seals, or use rudimentary forms thereof, such as, for example, metal Belleville washers placed back to back, etc. Because each track contains a large number of pins, the expense of a seal is an important consideration in adopting it.
Considering the design and use environment of crawler tractors and the track links and pins and bushings thereof, an ideal track pin seal is one which will accommodate a relatively great degree of axial dimensional variation, whether such dimension occurs as a result of cumulative tolerances in manufacturing (so-called "tolerance stack up") or results from stresses and strains in use, and of course, eventual wear. As a corollary of the foregoing facts, it will be appreciated that metal Belleville washer type seals or other seals having a high axial spring rate are not highly desirable for an application of this type. An ideal track pin seal is one which has an axial spring rate which is moderate or fairly low, and yet which will generate an initial axial force which is sufficient to insure that the seal can successfully exclude water and grit and retain lube, even under conditions of minimum load. Because of the ever-increasing cost of machine parts, and the high cost of maintenance and labor, there has been and still is a great need for a really effective track pin seal.
According to the present invention, a seal is provided which provides most or all of the advantages of highly expensive prior art seals, and which does so at low initial cost. The seal of the invention applies proven principles, but uses structures and materials which are different from the prior art and which provide new operating characteristics and advantages.
In view of the need referred to above for an improved, highly reliable low cost seal for track pins and related applications, it is an object of the present invention to provide a novel seal for track pins and similar applications.
Another object of the invention is to provide a track pin seal using a new combination of structures and materials adapted to provide reliable, long term life with low initial cost and virtually no maintenance.
Another object of the invention is to provide a seal which utilizes a novel arrangement of an end face, mating surface, and axial loading member therefor.
A still further object is to provide an end face seal using two different elastomeric materials, the softer of which provides an axial end load application and torque transmission capability in all types of weather conditions, and the harder of which provides outstanding wear resistance, with the softer element also providing a secondary or relatively static seal between itself, the harder member and the part of the track link in which it is received.
Another object of the invention is to provide a seal wherein the primary seal ring receives a radial compressive load from the secondary seal member, and which resists undue radial deformation by reason of having portions of such primary seal ring engage a part of the track pin itself.
A still further object is to provide a track pin seal in which the primary seal member is supported by a portion of the track pin, and wherein the seal ring includes means permitting passage of oil from a reservoir area to the interface between the primary seal ring and the mating part.
Still another object is to provide a track pin seal having a secondary seal member of generally annular form, having a cross section of a generally parallelogram-shaped configuration.
Another object is to provide a track pin seal having two pieces and adapted to be supported by a track pin or a member associated therewith, with the so-called secondary seal member being adapted to transform an axially applied load into a combination of increased radial compressive load and a partially reduced axial load.
A further object is to provide a seal unit having two pieces, one of which comprises a primary sealing ring of a tough, but resilient elastomeric material having excellent abrasion resistance, and the other of which excellent abrasion resistance comprises a secondary seal ring made from a softer elastomer, with the second ring being adapted to apply the loading forces necessary to create an effective sealing action.
Yet another object is to provide a seal which will survive a severe service environment while being made entirely of elastomeric materials.
A still further object is to provide a seal which will constitute an improvement over existing track pin seals, while at the same time providing greatly reduced costs.
Another object is to provide a seal unit in which the primary sealing ring includes an end face surface having a generally radially extending element and a frusto-conical element tapering radially outwardly and toward the member with which the ring will cooperate to form a primary, dirt-excluding seal.
The foregoing objects and advantages of the invention are achieved in practice by providing a seal unit having a generally annular secondary seal and force applying member of a characteristic shape, and a primary seal ring of a stiff, elastomeric material having a generally L-shaped seat for receiving the secondary member, and an axially directed end face portion adapted to contact a part of the track pin mechanism to be sealed, with the primary seal ring including plural axial passages extending between the axial ends of the primary seal ring to permit flow of lubricant therethrough even under difficult conditions.
The exact manner in which these and other objects and advantages are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, in which like reference numbers indicate corresponding parts throughout.